1. Field of the Invention
The present invention relates generally to the field of plastic pipes, and more particularly, is directed to an improved extruded pipe socket molded insert suitable for being encapsulated within the bell or socket at one end of a length of plastic pipe during the pipe belling procedure to provide a precisely formed interior recess for seating a resilient gasket therewithin.
2. Description of the Prior Art
It has been the common practice in the plastic pipe industry to form an expanded bell or socket at one end of a length of plastic pipe to receive therein the unbelled end of the next adjacent length of plastic pipe. A resilient gasket of moisture impervious material was installed at each joint for sealing purposes. This provides a sturdy interconnection between adjacent lengths of pipe in a manner to provide structural integrity and to prevent leakage at each pipe joint when a piping system is made up in the field. More recently, in order to improve the leak resistant characteristics of the system, an internal groove has frequently been provided in the bell or socket configuration when the bell or socket shape was formed. The internal groove thus formed presents a convenient, annular recess for seating a resilient gasket therein in a manner to fascilitate the making up of leak proof junctions between adjacent lengths of pipe without unseating or otherwise disturbing the gasket during pipe line construction.
The proper seating of the gasket within the hub or spigot of a pipe can sometimes present field problems upon installation, especially in large diameter work. Particularly, in many large diameter pipe hub designs, the gaskets have been subject to displacement or "fishmouthing" when the joint was being formed in the field. In other instances, when the system was operated under pressure, there are many documented instances wherein the gasket would blow out in the event of pressure surges in the line, to thereby destroy the integrity of the piping system as such joints.
In order to increase the reliability of the piping systems and to assure improved gasket seating in large diameter plastic piping systems, a novel extruded pipe socket molded insert has previously been developed by the present applicants. The molded insert is disclosed in U.S. Pat. No. 4,625,383, entitled "Method for Seating a Gasket in a Plastic Pipe Bell Using a Hard Configured Ring", which patent is owned by the assignee of the present application. The molded insert or "EPSMI" ring disclosed in U.S. Pat. No. 4,625,383 is designed for application upon the belling mandrel just prior to belling and then the bell or socket in the pipe end is formed about the EPSMI ring. In this manner the ring itself is utilized to shape an annular groove in the bell and the ring or insert will become encapsulated within the bell during the bell or socket forming operation. Upon properly forming the bell or socket on the belling mandrel, the belled end of the pipe is removed from the mandrel with the EPSMI ring encapsulated therewithin to thereby provide a hard plastic, precisely formed seat. This precisely formed seat is designed and intended to subsequently receive a resilient gasket therein in a manner to obviate the field installation and operating problems that heretofore were generally encountered with the prior art internal groove and resilient gasket constructions, particularly in large diameter plastic piping systems.
While the EPSMI ring disclosed in U.S. Pat. No. 4,625,383 has proved to be of great benefit in the large diameter plastic piping industry, the large volume of relatively high cost plastic material, such as polypropylene plastic, required to form such rings has proved to be expensive in use. Both the high material cost and the relatively slowness in manufacture due to the considerable cooling period required in the mold because of the thickness of the ring section have combined to increase the plastic ring production costs. The present invention seeks to provide a pipe socket plastic ring insert construction which results in considerable material cost saving, which is capable of increased production speed and which provides better efficiency in fabrication during the bell forming procedures.